1. Field of the Invention
This invention relates generally to marine seismic energy sources. In particular it relates to an improved marine seismic source that hydraulically reciprocates transducer plates to create acoustic signals in water.
2. Description of the Prior Art
The prior art includes several types of seismic mechanical vibrators which provide acoustic energy output in a body of water. These vibrators typically involve the use of pistons to transform electrically controlled hydraulic pressure signals to acoustic signals.
An example of such a vibrator can be found in U.S. Pat. No. 3,394,775, issued on July 30, 1968 to Cole et al. The disclosed system utilizes a hollow cylinder containing a piston that divides the cylindrical aperture of the cylinder into two chambers. Hydraulic pressure is applied alternately to the two chambers, and the pressure applied alternately on the two sides of the piston causes the piston to reciprocate slidingly along the inner surface of the cylinder. A plate is rigidly connected to the piston. As the piston reciprocates, the plate also reciprocates. When the plate is placed in a body of water, the reciprocation of the plate will impart seismic energy vibrations to the body of water. In order for the applied hydraulic pressure to be effective in driving the piston, the circumference of the piston must maintain sealing contact with the inner surface of the cylinder when the piston is sliding back and forth along the inner cylinder surface.
Other examples of vibrators using similar piston assemblies are described in U.S. Pat. No. 3,246,289 (1966) to Mellen; U.S. Pat. No. 3,403,374 (1968) to Mellen et al; U.S. Pat. No. 3,384,868 (1968) and U.S. Pat. No. 3,482,646 (1969), both issued to Brown et al. The parts in close contact may wear out and the vibrator may require regular replacement of parts.